When the following amino acids are separated by running them on agarose gel, at pH 7, which one of them will migrate slowest to the anodic end?
**Core Concept**
The migration of amino acids in an electric field is influenced by their charge and molecular size. At pH 7, amino acids will be separated based on their net charge, with positively charged amino acids migrating towards the cathode (negative electrode) and negatively charged amino acids migrating towards the anode (positive electrode).
**Why the Correct Answer is Right**
Glutamic acid has the highest negative charge due to the presence of three carboxyl groups (-COOH) that are ionized at pH 7, resulting in a net charge of -3. This high negative charge will cause glutamic acid to be strongly attracted to the anode, but its relatively large molecular size will hinder its movement through the agarose gel, resulting in slow migration.
**Why Each Wrong Option is Incorrect**
* **Option A (Arginine):** Arginine has a net positive charge due to the presence of two amino groups (-NH2) that are protonated at pH 7, resulting in a net charge of +1. This positive charge will cause arginine to migrate towards the cathode, making it faster than glutamic acid.
* **Option B (Histidine):** Histidine has a net positive charge due to the presence of one amino group (-NH2) that is protonated at pH 7, resulting in a net charge of +1. This positive charge will cause histidine to migrate towards the cathode, making it faster than glutamic acid.
* **Option C (Lysine):** Lysine has a net positive charge due to the presence of two amino groups (-NH2) that are protonated at pH 7, resulting in a net charge of +1. This positive charge will cause lysine to migrate towards the cathode, making it faster than glutamic acid.
**Clinical Pearl / High-Yield Fact**
At pH 7, amino acids with a higher negative charge and larger molecular size will migrate slower to the anodic end. This principle can be applied to other charged molecules, such as nucleic acids and proteins, which can be separated using electrophoresis techniques.
**Correct Answer:** C. Lysine